Besides TextUI.modelToView() and viewToModel() operation the View API should reflect specific aspects of editor view hierarchy such as lazy construction, non-EDT view rebuilds which implies a requirement for locking.
View SPI should allow to register custom view factories to build client's custom views.
When designing the editor.lib2/org.netbeans.modules.editor.lib2.view package I have assumed potential API/SPI classes. They will need some polishing but it should be more or less like this:
View API:
ViewHierarchy
LockedViewHierarchy
ViewHierarchyListener
ViewHierarchyEvent
View SPI:
EditorViewFactory
EditorView